Corrosion inhibitive cadmium phosphatechromate pigment

ABSTRACT

A PIGMENT COMPOSITION FOR PREVENTING CORROSION OF ALUMINUM COMPRISING:   PERCENT BY WEIGHT CDO 49.4 CRO3 19.3 P2O5 16.5 KOH 14.8   AND THE METHOD OF PRODUCING IT.

i r 3,591,399 O Patented July 6, 1971 3 591 399 STATEMENT OF THE OBJECTS OF CORROSION INHIBITIVE CADMIUM PHOSPHATE- INVENTION CHROMATE PIGMENT US. Cl. 106-301 2 Claims ABSTRACT OF THE DISCLOSURE A pigment composition for preventing corrosion of aluminum comprising:

It is an object of the present invention to provide a pigment having improved corrosion inhibitive characteristics when incorporated in a suitable primer and applied to an aluminum surface, particularly crevice areas thereof.

Another object of the present invention is to provide a novel anticorrosion pigment formulation for the protection of crevice areas on aluminum surfaces which is both economical and effective in use.

DESCRIPTION OF THE PREFERRED EMBODIMENT cdo T is invention includes a phosphate-chromate pigment c o 193 eompflslngi P t ercen 1 2%3:331:13::::::::::::::::::::::::: i335 Cdo 2O CrO 19.3 and the method of producing 1t. P 0 16, 5 KOH 14.8

STATEMENT OF GOVERNMENT 100.0

INTEREST The invention described herein may be manufactured The empirical formula is 6CdO'4 3 2 5' 2 and used by 0 for the Govern t of th Unit d State From the above description it is seen that the formulaof America for governmental purposes without the payn is a cadmium-potassium mined Cat on pigment Conment of any royalties thereon or therefor. taining 21 ml'Xed fihromatephosphate anion Y d In preparing t e present pigment the cadmium oxi e is BACKGROUND OF THE INVENTION dispersed in approximately four times its weight of water. (1) Field of the invention The chromium trioxide and phosphorus pentoxide are This invention relates generally to novel pigment comaddefl SIPWIY with Stlnmg and E Potasslum positions and more particularly to phosphate-chromate f l addefi as a 50% Solutlon P the H 15 pigments which impart superior anticorrosive characterstlrrlng 1S contmued 24 hours wlth Potasslum istics to primers when applied to crevice areas on alumidroxlde added to m m l the PH at between to num Surfaces. The supernatant llqllld is then decanted and the solid material is dried first on a vacuum filter and then over (2) Descnptlon of the Pnor art calcium chloride. The dried pigment is then ball-milled. There have been many pigment formulations developed 40 This Pigment along with other test Samples Were formufor use within various primer formulations, which, when lated into Suitable P The Pigment content was applied to aluminum surfaces, will enhance the protection lusted 011 the basis of Standard QiPadSOrPiiOI'I tests Using thereof against the insidious encroachment of corrosion. the Particular Specification Vehicle-Solvent IIliXtllre as the Heretofore the most successful anticorrosive pigments in- Formulations Were ball-milled for at least 24 hours corporated the use therein of chromium materials. Howbefore usingever such formulations were not entirely successful since The following table Shows the Corrosion results aluminum corrosion once initiated tended to spread tairled when the Present Pigment and specified test P rapidly, particularly in crevice areas or under blisters. The ments were incorporated into alkyd Primers which in turn present novel pigment formulation provides improved pro- Were P y on test p The test Perle1S Were Corltection at h areas, structed of aluminum, and were cleaned and deoxidized.

Countersink holes were bored in the panels and cadmium- SUMMARY OF THE INVENTION plated steel bolts inserted, using cadmium-plated Washers Thus, the present invention involves a novel phosphateand nuts. The panels were sprayed with the test coating, chromate pigment with the empirical formula of with a second coat applied along the edges by brush to 6CdO-4CrO -2P O -K O. This pigment when added to a eliminate edge effects. Panels were allowed to dry at least suitable primer will provide improved protection of alumione week before exposure. Before testing, the coating num surfaces, especially at crevice areas. was scratched near one edge.

TABLE I.RESULTS OF CORROSION TESTS 17 weeks Fastener area General Pigment panel Scratch Aluminum Cadmium Cadmium chromate 0 0 S M Zinc-cadmium ehromate 0 0 M S Cadmium ph0sphate-chromate. r 0 0 VS VS Cadmium silicate-chromate... S, B 0 S M Cadmium tungstate i M, B 0 S M Graphite S, B VS VS M Aluminum M Vs M H Legend: 0= no corrosion; VS= very slight corrosion; S=slight corrosion; M=moderate corrosion; H=heavy corrosion; B blistering.

The test panels were suspended around the periphery of the test vessel, /2 inch above the liquid level. The test solution was a 3% sodium chloride brine. For a period of minutes every 2 hours the brine was splashed onto the test panels. The brine solution was changed every 48 hours to prevent accumulation of inhibitive ions.

The graphite and aluminum pigments were formulated without inert fillers.

It Will be noted that the cadmium phosphate-chromate pigment of the present invention provided good protection to the general area of the panel. The corrosion protection in the fastener area was the best obtained with any of the primers tested. There was no corrosion on the cadmium plated fastener, and either zero or very slight corrosion in the various crevice areas.

The mechanism by which the cadmium-phosphate pigment operates is believed to involve the solubility thereof in water. If its solubility is too high the pigment will be leached rapidly forming blisters. If the pigment iTtBo insoluble, the concentration of the inhibitive materials will be too low to be eflFective.

The following table shows the results obtained on leaching of the present pigment and other standard pigments from alkyd primer films. The tests were run for three weeks in a 3% sodium chloride brine.

TABLE I1.-P RIMER LEACHING TESTS Composition of solution after 3 Weeks, p.p.m.

CrOt- Cd Other 252 For, 77

Pigment From the results it is seen that the cadmium-phosphatechromate is in a range somewhat similar to that of zinc yellow. However cadmium silicate-chromate leached to a much lower degree which probably accounts for the poorer corrosion characteristics of this material.

It is claimed:

1. A pigment composition for preventing corrosion of aluminum comprising:

Percent by weight CdO 49.4 cto 19.3 P205 16.5 KOH 14.8

2. A method for the production of a pigment which prevents corrosion on aluminum surfaces comprising:

dispersing cadmium oxide in approximately four times its weight of water,

adding thereto chromium trioxide with stirring,

adding thereto phosphorous pentoxide slowly with stirring,

adding potassium hydroxide until the pH of said solution is maintained at between 6.5 and 6.8 with constant stirring for 24 hours,

decanting the supernatant liquid,

drying the remaining solid material, and

milling the dried pigment, said oxides and hydroxide being in proportions to produce the pigment composition of claim 1.

No references cited.

TOBIAS E. LEVOW, Primary Examiner I. V. HOWARD, Assistant Examiner US. Cl. X.R. 106302 

